It does not look like ⿰女啟 should be read miau²¹. It seems possible that ⿰女啟 is a mistake for some other character. I think additional evidence is required in this case.

Andrew’s comment is right. The 建瓯 words in 《汉语方言大词典》 were collected from several unpublished books or article written by 潘渭水, such as 《建瓯的谚语（补）》《建瓯方言的谚语和俚语》《建瓯方言词语》. I can’t find these three ones, but I know 潘渭水 also wrote a dictionary on 建瓯方言, and I have checked it.

The entry shows 小⿰女畝 (WS2021-00993:UK-20820) siau21 miau21. “妾，舊時男子在妻子以外娶的女子”. There are also 小⿰女畝囝 siau21 miau21 kying21, “舊指妾生的孩子，在家庭中地位較低”. (李如龍, 潘渭水; 李榮: 《建甌方言詞典——現代漢語方言大詞典·分卷》, 南京: 江蘇教育出版社, 1998.12, ISBN 7-5343-3411-X/Z·90, p. 155) I don’t have a clear copy to show the original page.

00993

女 38.10.4

UK-20820

TS 13 · IDS ⿰女畝

I suggest UK withdraw this character if there is no more additional evidence, and I will add the language tag as mnp to WS2021-00993. If any expert has question or comment, I can try my best to ask Prof. 李如龙.

As a translation supplement,

Evidence 1 shows "小老婆", meaning "妾" (~concubine).
#13022 for "小⿰女畝" shows "妾, 舊時男子在妻子以外娶的女子" (~concubine, [historically] refers to a woman that a man married in addition to his wife).
#13022 for "小⿰女畝囝" shows "舊指妾生的孩子, 在家庭中地位較低" ([historically] refers to a child born to a concubine who has a lower status in the family).

The function for "妾" and "concubine" may be slightly different (cf. https://zh.wikipedia.org/wiki/%E5%A6%BE and https://en.wikipedia.org/wiki/Concubinage) but that is not important.

Based on the investigation by Eiso, UK-20807 is probably a mistake for ⿰女畝 (UK-20820), therefore we WITHDRAW this character.