I don't know how to feel or handle this

Elizabeth • Mommy of one beautiful girl, and twin boys (:
My sister is staying with me to help until I no longer need it. Well, we found out yesterday, she is pregnant. She had a miscarriage back in May at 8 weeks. I flew to Florida with my daughter to help my sister while she was pregnant, then the miscarriage happened. So thankfully I was there to support her mentally along with my mom and other sister. But here's my issue. She is not with the baby's father. Second time with this 'best friend'. He does not have a stable job, does not have a permanent address, travels the country though hitch hiking. I have never met him. Heard he's nice and all, but honestly, he is a bad influence on my sister. She ran away from home last year. She is going on 21. She is an adult. But she doesn't act like it. A baby, well, if she stays, my husband and I will be the ones taking care of it. I can't. I have a toddler and twins on the way. I will not be able to. I will be physically drained. Question is, do I just send her back home to our moms house, or do I suck it up and try to help? I don't want her to think I'm dumping her off on our mom, that I don't want her here. I would love to have her here, But I can't. It's too much. And we can't have the, father of the baby, here as well. Finacially, that's a no go. Gosh, I don't know what to do. I feel horrible for wanting to send her back to Florida.