Oh honey, it's OK. It's normal. Toddlers love the excitement of someone new. It does NOT mean she loves you any less, I promise!
I work full time, but I went through the same thing recently. My husband's whole family was visiting us and he took the day off work and kept our son home from daycare so his family could spend time with him. When i came home from work, my son was having so much fun playing with DH's fam he barely noticed me! i was crushed, not to mention a little embarassed, I mean I didn't want his family to think my son is not bonded to me.
I called my mom and guess what she said. She stayed home FT and did not work at all, and any time her best friend was around, all I wanted to do was be with her friend! I would leave my mom's lap to sit with her friend, and so on. This was when i was a toddler like you and I's children. It made me feel much better. (Mind you, my mom remembers this 25+ years later, so we are ALL a little hurt by it - and that is normal too.)
So anyway it's just the "novelty factor" of someone new who loves her and no doubt is fawning all over her. But YOU are still her number one. In fact, the fact that she can easily attach to new people means YOU have done a great job making her feel secure and trusting. Good job mom!