Veer Begum ji, So am I.
There are 376 references to the word "mother" in Siri Guru Granth Sahib. However different words are used to refer to "mother" and the context can make the meaning change. This is the case with many eastern languages, including Punjabi and Gurmukhi -- where implication rules.
All this means is that words say more than the literal translation would state directly. And the literal meaning of a word is likely to change even in casual conversation. Implication is found in every language, but some languages depend on implication more than others, and Sanskrit-based languages like Gurmukhi are at the upper end of implication use. Turkish (in a different language family) is probably the most extreme example of a language where implication is as important as grammar in written and spoken communication.
So sometimes the word maath is used and makes a comparison to an earthly mother. As on Page 203 Line 10 Raag Gaurhee Bairaagan: Guru Arjan Dev:
mwq ipqw suq bMDpo qUM myry pRwx ADwr ]
maath pithaa suth bandhhapo thoon maerae praan adhhaar ||
You are my mother, father, son and relative; You are the Support of the breath of life.
Or, sometimes we see a phrase like this, where mother is understood to be the Mother - Soul. Page 226 Line 13 Raag Gaurhee: Guru Nanak Dev:
nwm ibnw ikau jIvw mwie ]
naam binaa kio jeevaa maae ||
Without the Naam, how can I live, O mother?
And there are other words for mother as well with various meanings. In fact someone could write an academic paper about the uses of the word mother in SGGS dev ji, and contribute to the world's understanding of Sikhi.
Until we know which line you are talking about Baldir ji, the mystery will not be solved.
BTW - The question, Does God have a brother? would go hand in hand with this discussion. There are 80 references to brother in Siri Guru Granth Sahib, with equally interesting implications.
Bye for now... and humble apologies to all speakers of Punjabi who could explain the part about implication better than I.