dobi underweight

[Guinness' mom]

My sister-in-law has acquired a second dobi...I would call it more of a rescue (even though they are expected to pay for it :sad
This poor female is about 15 lbs UNDERWEIGHT....she has not been properly exercised if at all (the women she got it off of has "health issues") She even made a comment that the dog had not eaten in 2 days so in other words she probably ran outta food and knew she was getting rid of the dog so didn't want to put out any money. She is the most gentle creature you would ever meet she seems so tiny and frail...you can tell her back end needs some major exercise as she seems to not be able to hold it completely upright and you can see her prominent bum bones.
My sis-in-law was told by a friend to feed in Mac and cheese for about 2 weeks to help put on weight . I am looking for any advice you all may have. I did notice some whitish discharge coming from her vaginal area so I am guessing she may be coming into a heat very soon as well and they have an intact male dobi. So we are all really worried about this cute little thing the last thing she would need is to get pregnant is her unstable condition.