I think that To Be Loved and Brinny have given you excellent answers.
But I will see how I can offer a little, too, here >
An old friend of mine from Philadelphia asking for forgiveness.
Well, if she is in another location, it could be as simple as forgiving her and then she is not around, anyway, to be trouble. But yes forgive her, but test if and how to trust her.
It was my husband himself whom told me that "she was on his heels"(well he used a different word) basically she was pretty obsessive over him when she had her own relationship and daughter to tend to.
So, if she is still not a Christian, or even if she is, she still could have the ability to get hung up about your husband. So, I would be very careful about if and how you help her to be involved with him and you. I suppose you can tell her you forgive her, but you are concerned about where she is at, about certain things, and ask her to please be ready for however you take precautions. And if she is sincere, I think she will be ok with this, or even welcoming you to make sure about her. But make it clear you do love her and forgive her, but you need to make sure about what is good for you two, now.
Plus our friendship consisted of doing drugs together while her boyfriend sold them. The girl and I fought about it and it ended in us not being friends anymore.
Well, if she is asking forgiveness about this, possibly she now appreciates she was wrong and intends to not be into that stuff, any more. But if she is trying to use "forgiveness" to open a door for her to use you . . . don't cooperate with what is wrong. If she is in another city and wants to spread drug business to where you are, she could be trying to use you as a way to have a place to stay while she is selling in your area. So, prayerfully test. I don't know all the details, and maybe you don't know a few
Also, she might ask forgiveness about the argument about drug dealing, but she might not want to call your attention to her interest in your husband . . . keep attention to the drug thing, in order to keep you from evaluating what her motives could be about him. But, like I say, I don't know. So, also, you might share with your husband about this, and pray together, if you both are into spiritual sharing and ministering, and agree to not let either of you, maybe, get alone with her where she can work her motives. Keep together with each other.
Do I invite her with open arms because God forgives and so should we? Or do I distant myself away because she may be harmful to my family?
Our Father has forgiven us, and now He is correcting us > Hebrews 12:6-11 > so, He has not just given us "open arms" for us to do whatever we jolly well please. He does see how we need correction, I can see from Hebrews 12:6-11. But, then, also, God does not distance Himself from us, but if we go the wrong way we are getting away from Him and He may arrange for people and things to resist us so we don't keep going the way Satan is taking us >
"God resists the proud" (in James 4:6, 1 Peter 5:5).
So, I would say open arms and distance are both extremes which are not correct! You do not have open arms without limits, but also you do not keep an impersonal distance. But test prayerfully, and possibly as you keep to living right she might just disappear if she is not spiritual for sharing things of God with you, even if you are good with her.
Test her with your good example (1 Peter 5:3, Galatians 6:1, James 5:16), and see if she feeds on your good example or leaves the dinner table
