Labrador puppy help please?

Sorry for the not so great title, anyways. I have two mini dascshunds and now a labrador retriever puppy. Everything has been fine except for the mini dascshunds. The youngest dascshund Izzy, is scared of him and seems to be threatening to attack him. He only wants to play with her but, she doesn't understand and goes crazy trying to bite his neck. Luckily, I've been there to stop her though. My family doesn't know if we should get a trainer or if we should just let her get used to him and discipline her. The other one Spots, isn't as bad. He did try to bite his neck though. So...what do I do?