Most Helpful Guy
Do not lie.
TRUTH NOW = MAY RUIN YOUR RELATIONSHIP.
LYING NOW = __WILL__ RUIN YOUR RELATIONSHIP.
The moment you get on the bad side of the mother-in-law, your relationship is over. You will get on her bad side once she finds out you lied... and SHE WILL find out you lied. At that point, she will do whatever is necessary to break up the relationship because, as a liar, you are no good for her, her child, or her family. You are no longer trustworthy and could go against the family and, as Michael Corleone said to Fredo:
Most Helpful Girl
Sounds unreasonable. How are you gonna hide what your profession is? What is your profession anyways?