forefather 49048
foremother 3404

Sounds a bit odd and PC to me, I wouldn't block it.

https://www.jstor.org/stable/23896397
(1976 mention of the word)
https://books.google.com/ngrams/graph?
content=forefather%2C+foremother%2C+foreparent
&year_start=1800&year_end=2019&corpus=26&smoot
hing=3&direct_url=t1%3B%2Cforefather%3B%2Cc0%3
B.t1%3B%2Cforemother%3B%2Cc0%3B.t1%3B%2Cforepa
rent%3B%2Cc0
(google books English corpus ngrams results 
for forefather, foremother and foreparent)

I've never come across it either, only 
surmised it might exist and it turns out it 
does. I don't think having it detracts 
anything from the entry. I know that 
forefather is applied to ancestors of both 
genders but opposition to an obviously 
masculine gendered word covering everyone is 
why we now also have so many woman-specific or 
non-gendered words like "ombudswoman" and 
"ombudsperson", and this. I don't think 
throwing people who deeply care about these 
kind of things a bone is a bad thing, at least 
not when there's clear evidence the word is 
already accepted by other dictionaries.

I don't think it's needed. This is the first time I've seen "foremother", and English dictionaries treat "forefather" as a synonym of "ancestor" (not male ancestors specifically).

the word appears in both MW and Cambridge
https://dictionary.cambridge.org/dictionary/english/foremother

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

gg5

@@ -18,0 +19 @@
+<gloss>forefather</gloss>