What to do about RD..... I'm at my wits end

Ok ladies.. I bring the subject to you since my FH is asking me to. He's such a wise man for knowing where to find the answer. So here is our little dilemma:

Tradition has it that the grooms family hosts the Rehearsal Dinner. Well, due to some financial worries and a few house repairs that are not finished, we decided (FMIL, FH and I) that I would ask my dad to host it. My parents are divorced, and since my dad is often left by the wayside with being involved, I thought this a nice thing to make 'his own' and let him feel a part of the wedding. Well..... 2 months after I asked him to do it, and he was excited and said yes, NOW FMIL tells FH that she is hurt that she isn't hosting the dinner. I don't understand.... we had this discussion over and over and we all decided it would be best to have it at my dads. Now she's changed her mind, and wants to do it. I told FH that I am not asking my dad to cancel his plans, so if it really means that much to him and his mom, that HE should bring the issue to my dad. What would you do? I really appreciate your opinions, and I know you ladies are the right ones to come to about this. TIA