@Chris Collins excellent tips for when applying.

I'd like to create an official rent contract applied to the room they'll be staying in, but want to ensure this is fine within context of the loan (assume primary occupancy still valid since only renting room).

The Rider reads: "This form applies only if form 3522 1/01 are used" (it was).

I'm curious, why didn't you and the tenant apply way before it got to this point? 

We got to the page that says:Due to the number of members in your LLC, you are considered a Multi-Member Limited Liability Company (LLC) as the type of structure applying for an EIN.Since you are a multi-member LLC, we must initially classify you as a partnership.

Triplexes specifically are harder to come by, but your same idea can apply to a duplex or quadplex.To echo a great point though: even if you are not positively cash flowing in year 1 (maybe even 2), you are still DRASTICALLY reducing your monthly payments and saving lots of money a year.

In either scenario, my friend and I would either be applying for a loan together, or I would apply for it under my name only.

Same concept applies here.

It doesn't sound like you're trying t apply pressure at all and that a reasonable date - maybe 30 days as she did pay first month (just a thought, obviously not legal advice) rent would be enough for both parties. 

You have 3 very different treatments:deducted immediatelycapitalized and later depreciated as part of the property acquisition costnot deductible at allWhich one applies under which circumstances is not only complicated but also controversial.