Tell her that she should let the Holy Spirit guide her instead of some regular blokes on the Internet. MHFM will lead a lot of souls astray, it's a poison to Catholicism.

And what priest have you recommended her to?

Go and dine with the prots and show your Catholic side!   Don't jam anything down their throats but be gracious & happy.  How else are they going to see Catholic action in action?!
There's nothing wrong with dining with prots.

... that she should not interact with her protestant family any more. I know our Lord stresses the importance of dogma and said that He will divide like a sword, but can she put the differences aside and still dine with her family this weekend? She's in terrible shape.

I'm not going to say MHFM is right or wrong here.  Is there more to this story?  Because I'm guessing there is.

MHFM said the right thing in my opinion.

"Go not into the houses of heretics".

About time she got her own place.

"There is no one who has left land and husbands and wives and sons and daughters in this life for my sake and for the gospel who shall not in this life and in the next recieve a hundred times more husbands and wives and sons and daughters and life everlasting" ( or something like that).

Basically I have a faithless family, and ever since I cut them off my faith is stronger.
They were holding me back, as the pagans also hold this girl back.

MHFM just told her the truth.

We have enough heretics in the world, shoving divorce, fαɢɢօtary, cohabiting, etc down our throats that that last thing we need to do is outcast all Protestants in our life especially family. If i did that, I would have no family at all and be divorced. You sound cultish and that's not the teachings of the church at all.

Protestant christains aren't pagans.  You've cut your family off for other reasons, I've read your posts. Don't act like you did because they are pagans. And don't encourage others to do the same.

Basically I have a faithless family, and ever since I cut them off my faith is stronger.

They were holding me back, as the pagans also hold this girl back.

I would put this into the category of an evangelical counsel, a supremely praiseworthy ideal, but it's something that also has to be offset with prudential considerations regarding actual situations.

Let's say I had a heretical relative whom I felt that by being around I could possibly bring closer to the faith (someone who posed absolutely no danger to my own faith), or someone who had health or financial problems, someone who had emotional or mental problems.  I would still feel obliged to help them even if helping them meant spending significant time with them and maintaining certain social connections with them.  If on the other hand, I prudently judged that breaking ties with them would be helpful to make a statement to them regarding the gravity of their actions or if I needed to break ties with them because they were harming my own faith, then that would be a different situation.

So I do consider it irresponsible of MHFM to be giving this kind of advice when they really don't know anything about the real world factors that would weigh into making the prudential judgments that would be required to navigate this situation in the best way.  So, for instance, what if the person to whom they gave this advice were prone to scruples or might be inclined to get severely depressed (which could then cause damage to the person's soul).  It's one thing for someone to make the best decision for themselves, knowing the pros and cons, but quite another to throw this stuff out there without any pastoral knowledge of the person's situation.

So a prudent spiritual director might realize that in one person's case, they should be required to break ties with relatives, whereas in another's case, they might be much better served (and their relatives better served) to maintain these ties at least at some level.  There's no absolute black and white on this matter IMO.

I so agree with you, Ladislaus!

If it's just a matter of dining with prots with no danger to your faith, there is no harm in that.

Christ was teaching us in Matt. 10 that if dining with prots means that you were choosing them over Christ, then of course you MUST choose to follow Christ.  However, Christ never meant us to be insular.  That's how cults start.  We are to be IN the world but not OF the world - a delicate balance.  (Yes, there are those few who are called to be hermits or cloistered).