Yes, she can bring the lawsuit in the sense that the child, as someone who presumably would have inherited had the house not been transferred to you, has "standing" (a sufficient legally recognizable interest) to challenge the deed. IF the child can prove that the deed was void, she can undo it.However, while she can bring the lawsuit (the courts do not prescreen lawsuits for validity--therefore, as long as a lawsuit on its face appears to state a legitimate question or issue, it can initially be brought), if the county assessor oversaw or approved the transfer *and* your ownership was accepted by the court in the legal action to remove squatters, it is *very* unlikely that she would be able to prove that the transfer was invalid.