Providing concrete info is the only way you can take a serious 1st step.  

By hybrid I mean, it is a manufactured home with several additions surrounding it by either a concrete foundation and wood structure or peer and beam and wood structure.

Now, she went on my property (transpassing) without consent, dug it up, took out the an oil tank that was perfectly fine, filled back up the whole just with dirt and stones not even putting back concrete like it was before, and asking us to pay 50/50, which btw, she claims it cost her $12,000 and wants us to pay $6000, the price itself doesn't make sense.

@Joseph Lee,If it was me, I'd talk to the local code inspector and verify that what you propose is legal, within the existing zoning and within limits given the existing structure.You're going to be tearing up the concrete slab to put in the needed plumbing.

It is in a 50 year old condo and the concrete floors are dry. 

The loan that is listed is not concrete, Owner financing may be possible.Thank you for all feedback.

Some of the floors are already uneven.Here's the kicker (maybe): the house is not wood framed but rather has concrete block all the way to the attic.

Copper pipe installed incorrectly in concrete (like many were years ago) have a corrosion problem.

Dealing with plumbing in slabs is a mess, just make sure your budget accounts for the extra work involved for demo and then repouring the concrete. 

I'm sorry if there's not a ton of details, but I think I'm looking at high level solutions vs concrete ones to start - get gears turning, you know?