Women with no respect

I'll try not to make this too long, but would love advice.  Hubby and brother not very close, but my daughter and BIL's brother are best of friends/cousins.  BIL raised daughter himself for years and about 6 months ago met a girl who he moved in and now she raises the daughter while BIL works on the road.  BIL likes the fact that the new girl takes full charge and he can kind of just come and go or whatever, work all of the time, not deal with family life, I think.  So, new girl is the typical several kids by several different men, dated two of BIL's friends before they got together, man jumps a lot, doesn't work, just lives off of them an and seems to be looking for the next best thing.  I have only been around the new girl a couple of times and she never spoke to me or hubby.  Just went and sat in her room, not sure why.  Well, new girl is quite immature, takes the 13-year-old step-daughter "riding around" late at night, blaring music, etc, acting somewhat like a teen herself.  Well, niece was at my house a couple of weeks ago and the new girl comes by to pick her up (11:00 at night) and asks if my daughter can come too (My daughter is 10).  I was in bed actually and my daughter came and asked and I said No, it is late and she doesn't need to go anywhere.  Well, hubby was in kitchen and the girl asked my niece to call hubby outside.  He came out and she starts asking him why I didn't like her?!?!  Hubby told her I don't even know her and we just didn't want our daughter going anywhere at 11 at night.  

So, then a few days later niece called hubby's phone from the new girl's phone and asked hubby if she could come over.  He said he would check with me to see what plans we had.  I got hubby's phone to call niece back and just hit redial, which called the new girls phone.  When she answered, she did so in a flirty, sweet voice and as soon as I said hey and told her who I was, her entire tone changed.  I thought it was wierd, but once I got off of the phone I realized she thought it was my hubby calling her back, not me.

So, we go out to the house a couple of days ago to pick up niece and new girls comes out to the car and starts walking towards driver's side and saw I was driving and then goes to passenger side.  She tells my hubby that she made him a cd and she can make him more, just let her know what bands he wants.  She says not ONE WORD to me, not hi, nothing.  I don't even comprehend how a woman can be so disrespectful to walk up and talk to a married man, wife sitting there and not even smile my way.  I was so mad, I was about to seriously give her a piece of my mind, but I KNOW for a 100% fact that if I do that, she is immature enough that she is going to stop niece from coming over and that is my daughter's best friend.  I am going to hurt the kids by saying anything.  

Hubby pointed out to me the awkwardness of everything, I didn't even have to say anything to him, but his philosophy is no matter how much she flirts, it wouldn't work, so no need to worry about it.  My philosopy is I trust my husband 100%, but it is VERY HARD to sit there and let a woman disrespect me that way!  Last night niece was over and came to our room and told us the girl had called and said to let my hubby know she was bringing him another cd.  I mean, we didn't even ASK for one, she just randomly came over to bring him one.  I told niece, very nicely, that hubby uses his IPOD for music and we didn't want to trouble the girl, so just let her know we really didn't need anymore cds.  I honestly should say something to her myself, but I am just afraid it will hurt the kids, due to my frustration and I will probably lash out more than I should.

Anybody have any suggestions?