Okay do this- get a flexi lead, and she is on the lead- the lead connects the dog to you and helps you discipline the others. As soon as one starts to go for her, you correct that dog. Most dogs respect a lead.
Also letting her play with one other dog will help. Believe it or not- the fact is - they could be disciplining her for being so " shy"- .. When in my shepherds, one would go to jump a subdominant member- I flatten to the ground the aggressor, both dogs then are on forced down stay!
I have more but what breed are the dogs- and the ages please, and tell me who is more likely the instigator of this behavior.