That way the relationship might go smoothly, but they would always do what MIL wants and never what LadyL wants. What type of relationship is that? Definitely not an equal marriage in my eyes.
I wrote a reply but it didn't post for some reason so I will try to write it out again.
I agree it would not be an equal marriage. It would not be a marriage I would be happy in at all, but I also would be very unhappy in a marriage where I am constantly battling both my MIL and my DF. If it were me, I know what I would do (not marry DF because of the way his relationship
with his mother negatively impacts his relationship
with me) but I am not LadyL, and I suspect she truly does want to marry her DF.
If LadyL intends to go forward with the marriage, she can choose the hard way (standing her ground, constant battling with MIL and with DF) or the easier way (swallowing her pride and appeasing MIL so that her life with DF goes more smoothly). Neither choice sounds appealing to me at all, which is why, if it were me, I would call off the marriage.
But since LadyL DOES want to marry her DF (and I am not at all faulting her for that, I just know I would not be able to handle these particular dynamics) she has a choice to make: 1) stand up for herself knowing that she is unlikely to ever see positive change from either MIL or her DF and will be constantly battling them, or 2) appease MIL and DF and silently seethe, or 3) just let it all go and recognize that she cannot control her DF or her MIL so it is best to comport herself to rock the boat the least.