The 男の娘 Wikipedia article does include 男のコ in the list of variant forms but looking on Twitter, I'd say it's mostly used with the regular "boy" meaning. I'd make it a search-only form.
I don't think we need the むすめ reading. Wikipedia only mentions it in a note (「おとこのむすめ」と読む場合もあるとされる) and the source is an English Kotaku article.

@@ -12,3 +11,0 @@
-</r_ele>
-<r_ele>
-<reb>おとこのむすめ</reb>

男のコ	55090	83.6%
男のこ	6080	9.2%
男の娘	3699	5.6%
おとこの娘	470	0.7%
男の子	6097488

We currently have 男のコ as a form in our 男の子 entry (1420010). Looking at the WWW pages using it, it probably would be more appropriate here. Any view on this?

I think this is written w katakana too? 
https://www.cmoa.jp/title/115021/

I'm comfortable with that. I hope it wraps it up.

https://dic.pixiv.net/a/男の娘
"現在、女装していない男の娘もでてきており、女装必須というわけではなくなっている。"
https://numan.tokyo/words/NrlHS
"まれに男の恰好をしていてもかわいらしすぎて女の子にしか見えない男の子のことも指す。"
https://www.tukinasikotonoha.com/otokonoko-zyosoudansi
"確かに「男の娘（おとこのこ）」と聞くと、女装をしなくても女の子に見える中性的な顔立ち、という印象を持ちます。"
https://en.wikipedia.org/wiki/Otokonoko

Crossdressing doesn't appear to be a requirement (but presumably applies in the vast majority of cases).
The Japanese Wikipedia article on 男の娘 lists 10 definitions from various "専門家" and the only element that is common to all of them is "feminine appearance"/"looks like a girl".
The English Wikipedia article uses "feminine gender expression", which I think fits well.
Although it originated as a manga term, I don't think "esp. in anime or manga" is true any more.

@@ -19 +19 @@
-<gloss>young crossdressing male (esp. in anime or manga)</gloss>
+<gloss>young male with a feminine appearance (esp. one who crossdresses and has a feminine gender expression)</gloss>

https://numan.tokyo/words/NrlHS
女の子にしか見えない男の子のこと。

https://www.oricon.co.jp/special/59491/

https://www.japanesewithanime.com/2018/02/otokonoko.html
In Japanese, otokonoko 男の子 means "boy," literally "male child." This post, however, is about otokonoko 男の娘, "male girl," an Japanese anime slang for boys that look like girls, that translates to English as the anime slang "trap," or the gay slang "femboy."
https://www.j-cast.com/2020/08/16392220.html?p=all
「男の娘」を指す「trap」は差別用語？　海外掲示板の処置に日本でも物議
女性のような外見や内面の男性を指す用語として、海外のアニメ掲示板では「trap」という語が用いられることがあった。

urban dictionary's definition of trap:
A crossdresser, usually a fictional character in an anime, who dresses up in the opposite gender's clothing to trick people into thinking that they're the opposite gender.

Looking at Google Images, I don't think "young male who has a feminine aesthetic" is a very good gloss at all, I think it's too vague as to miss the point. The pics are all of crossdressers who would only pass for girls. (maybe half are manga/anime, half are photos). It seems the word "trap" came about to describe the exact same anime/manga phenomenon as 男の娘 did. There's apparent there's concerns it's derogatory because of the implication of "falling into a trap" or "luring into a trap" and this is a connotation the original Japanese doesn't have, true, but I still think it's weird to leave it out.

@@ -19 +19 @@
-<gloss>young male who has a feminine aesthetic</gloss>
+<gloss>young crossdressing male (esp. in anime or manga)</gloss>

https://en.wiktionary.org/wiki/男の娘

Probably fine. Wiktionary has it.

@@ -19 +19 @@
-<gloss>young man who has a feminine aesthetic</gloss>
+<gloss>young male who has a feminine aesthetic</gloss>

Is that really a good fit with 男の娘? I'm reluctant to fiddle much with Robin's 2019 gloss.

https://www.collinsdictionary.com/us/dictionary/english/femboy

@@ -19,0 +20 @@
+<gloss>femboy</gloss>

"trap" is clearly derogatory slang, so it would depend on the offensiveness level of 男の娘.  i'm not familiar with this term, but given that it's an extended wikipedia entry, it's unlikely to be derogatory slang.  i didn't read the article but there's nothing in the lede that suggests it's offensive

https://dic.pixiv.net/a/男の娘 
"あくまで、娘に見える可愛い男性のことなので、女装してる必要は無い。"
---
男の娘	        3699
おとこの娘	470

I agree that "trap" isn't a good gloss. However, I also think the descriptive gloss isn't entirely correct. The above article notes that a 男の娘 doesn't necessarily wear female clothing.
How's this?

@@ -5,0 +6,3 @@
+</k_ele>
+<k_ele>
+<keb>おとこの娘</keb>
@@ -16 +19 @@
-<gloss>man cross-dressing as a (young) woman</gloss>
+<gloss>young man who has a feminine aesthetic</gloss>

なるほど.

https://www.glaad.org/reference/transgender - The Gay & Lesbian Alliance Against Defamation

"Defamatory: "deceptive," "fooling," "pretending," "posing," "trap," or "masquerading"
Gender identity is an integral part of a person's identity. Do not characterize transgender people as "deceptive," as "fooling" or "trapping" 
others, or as "pretending" to be, "posing" or "masquerading" as a man or a woman. Such descriptions are inaccurate, defamatory and insulting. (See 
"passing" and "stealth" as problematic terms above.)"

The term "trap" has a strong negative connotation in English and is considered by many communities to be a hateful slur against transgender 
persons. This specific connotation detracts from the actual definition of the word, prompting its removal. The simpler, more descriptive 
definition is sufficient.

@@ -16,2 +16 @@
-<gloss>trap</gloss>
-<gloss>man crossdressing as a (young) woman</gloss>
+<gloss>man cross-dressing as a (young) woman</gloss>

I'll just go ahead and approve.

google images

"trap" is correct, I think.
https://www.urbandictionary.com/define.php?term=Trap

@@ -15 +15,3 @@
-<gloss>otokonoko, male daughter, a man who cross-dresses as a woman</gloss>
+<misc>&sl;</misc>
+<gloss>trap</gloss>
+<gloss>man crossdressing as a (young) woman</gloss>

https://ja.wikipedia.org/wiki/男の娘
https://en.wikipedia.org/wiki/Otokonoko
https://kotaku.com/what-is-japans-fetish-this-week-male-daughters-5804979

@@ -9,0 +10,3 @@
+<r_ele>
+<reb>おとこのむすめ</reb>
+</r_ele>
@@ -12 +15 @@
-<gloss>?</gloss>
+<gloss>otokonoko, male daughter, a man who cross-dresses as a woman</gloss>

@@ -8 +8 @@
-<reb>おとこのむすめ</reb>
+<reb>おとこのこ</reb>

https://ejje.weblio.jp/content/男の娘

Weblio has this as "trap" but there has got to be a better term