I don't think you need to worry. It's just her way of being excited. Dogs all show their excitement a little bit differently, and some are vocal about it.
The lab next door to us does these strange "half-howls" when the grandparents come to visit. He loves them to death. I have Dachshunds, which as a breed tend to be very vocal in general. One of my dogs has these funny sounding "excited barks" that are completely different from her ordinary barks or play barks. My other dog will sometimes whine a bit when exceptionally excited, but again, they sound nothing like her ordinary whines. They'll stand there wagging their tails and doing their excited "tap dance" with their front feet, and one will be doing these bizarre sounding barks, and one will be whining in a weird way. I'm sure it would seem pretty strange to someone who didn't know them!