How much should fmil be involved?

There is no particular etiquette. It’s whatever you’re comfortable with.

I agree with Kelly, totally depends on the relationship between the two of you. Traditionally (at least where I live), FMIL's do get invited to wedding dress shopping, get ready the morning of, and attend/plan the bridal shower. I'm inviting/have invited my FMIL to everything I just mentioned based on our relationship.

My FMIL and my fiancé’s two sisters will be getting their hair and makeup done with me. However, they’re planning to go first and then spend the rest of the day with my fiancé as he gets ready (he’ll be getting ready at their AirBNB).

I'm not having my MIL get ready with me. She doesn't really want to anyway. She wants to be surprised by how I look. I asked her if she wanted to come see me before my first look with my fiance and she said she would think about it. I don't think she will see me until we get to the Chapel. She is heading up the wedding favors and escort card pinecone holders. She also hosted my bridal shower, so she has been plenty involved.

My fmil has come to just about everything. If my mom was there she was also there.

My FMIL went to 2 venue tours, 1 catering tasting, we shopped with (and bought) her for her dress, she went to my bridal shower, she got ready with the bridesmaids & my mom (as well as my husband's stepmother), she went to the rehearsal & rehearsal dinner, etc.

Whatever you are comfortable with. I did not invite my MIL to get ready with us.

It really depends on your relationship with FMIL! If you'd like to have her get ready with you, that's fine - if you don't feel comfortable, that's fine too

Despite what some people would have you believe, you don't have to have her involved at all if you don't want. If you are comfortable with her in the "get ready room", then invite her. If you're worried about it being overly crowded, then don't!

I agree with PPs. It is more about what you want since its your big day. you could always offer for her to be there and let her decide. If there is something specific you'd like her to do then i would discuss that.