1) I cannot decide which Roma pass to get. My friend (is getting the
3-day pass). However, we will only be able to use it 1 full day so i'm
having a hard time wrapping my brain around the price. We will
definitely visit the Collosseum, etc but have not decided which other
activities included in the pass.
The Roma Pass is definitely not a good purchase for only one day. It's a questionable purchase even if you have the FULL amount of time to use it if you don't want to see enough of what it covers to make it pay, can't fit enough attractions into the time that you have, and/or don't take public transit frequently enough. As with any pass, it's a matter of doing careful math.
2) Do the Roma passes allow you to skip the line? Is there anyway to
skip the line together even if she gets the 3 day pass and I get the 2
day?
The pass allows you to skip ticket lines but not security-check lines at attractions which require them; there is no way to skip those. There are really only a couple of places where queues are a big problem: the Colosseum and Vatican Museums. The Roma Pass does not cover the Vatican, and ticket queues at both can be avoided by pre-ordering tickets from their individual websites. Galleria Borghese requires advance reservations even if you intend to use the Roma Pass at that one.
3) Which events are most expensive that would help me justify the 3
day price?
The 'most expensive' attraction doesn't justify the choice if it's not something you will enjoy. Choose the things you wish to do/see and THEN decide what the best method of entry should be.
4) Are there any discounts available for the Roma pass?
Not that I'm aware of.
