How to privately purchase a property from a buyer with a mortgage balance

[Alex Collins]

Hello!

Backstory: As some of you know based on previous post of mine I've found my first "possible" real estate deal.  A co-worker of mine is selling her condo (which is not listed on the market) and is allowing me first dibs. It's 3 bed 2 full bath and 1,300 sqft. Currently valued at ~180K. She still owes 57k on her 80k mortgage. Although it's valued at ~180k I'm thinking about offering her 90K because it needs some work. Both bathrooms need a complete remodel as well as the kitchen, the ceiling in 2 of the bed rooms are bowed (previous roof leak that was fixed) so new ceiling drywall, appliances, flooring, and paint throughout. I'm assuming I'll need 35-40K for the rehab which would bring my investment total to around ~130K. I've already had a home inspection done and it basically told me what I already knew about the property. I'm now looking into having a title company do a comprehensive title search before officially putting in an offer. 

If I was to purchase the property from her without realtors involved on either side how would I do so?  What are the pros/cons of doing a deal in this manner?