I sort of agree with Great Pyr. Since Jenny doesn't really know your mom, and she just walked in the house without you letting her in, it's understandable that Jenny acted the way she did. She was alerting you to let you know, "Um, mom some strange woman just let herself in our house!!!" She was also alerting the "intruder" that, "hey, this is my house and I didn't say you could come in. Stay back!" I think the main thing is, that once you told Jenny it was ok, she calmed down. That's very important.
Now, if your mom was a regular at the house, I'm assuming Jenny would not do this. If she did, that is something I would not allow, since she would be fairly familiar with her. Also, if your mom knocked on the door, and you went to greet her at the door, and Jenny still acted that way, I would not allow that either.