If the home is your mother's main home, she will probably qualify for the Section 121 exclusion (up to $250,000 of that gain, or $500,000 if she is filing a joint return with her spouse).
See https://www.irs.gov/taxtopics/tc701
Although your mother, as the donor of the gift of $90k, will probably not owe any gift tax, she will have to file a gift tax return since the amount exceeds the annual gift tax exclusion of $15k for the 2019 tax year. You, as the donee, will have no tax liability whatsoever on the gift.
See https://www.irs.gov/businesses/small-businesses-self-employed/frequently-asked-questions-on-gift-tax...
