Originally posted by Glacier
Couple things popped into my mind--one, since Riley is really young, it could just be a weird puppy phase. Lots of dogs go through a stage where they act like human babies "making strange".
That was my first thought also. Here is something from one of the behaviorist members on the forum English Mastiff Online...

These are the approximate ages when dogs may go through fear periods:

7-8 weeks
6 months
9 months
12 months
18 months
24 months

Not all dogs have fear periods and not all dogs have them at every age. Dogs have been fear-less until 18 months when they experience their first fear period.

You know your dog is going through a fear period when your dog becomes reactive to something or several things that she wasn't reactive to yesterday. This can be anything from a ball to a person to a flapping garbage bag.

Back down on your dog's exposure to new things - in fact I would strongly suggest that your dog not be exposed to anything new until the fear period is over. A new fear imprint can be very difficult to counter-condition. This is not the time to take the dog to the county fair, the kid's soccer game or petsmart. Only take the dog out to quiet places.

If your dog is suddenly fearful of an object, the fastest way to get your dog over the fear is to toss treats at the object. First, toss them far enough away so your dog is not afraid to eat them. This could be 3' or it could be 30'. Gradually toss treats closer and closer to the object until the dog is happily eating treats right next to the object. Once you do this, you will rarely have to toss treats at the object again, but sometimes you do.

If your dog is fearful of people, don't push your dog. If you are out, say the dog's name and then say "this way" and calmly lead your dog away from the person. By saying the dog's name and "this way", you are making the decision to move away from the 'scary' person. Your dog will learn to trust you more.

If you are at home, do not put a lead on your dog - leads restrict movement and if your dog can't "flight" his only other option is to "fight". You don't want to set your dog up for that kind of reaction.

Do not force the dog to greet or be petted by anyone. If the dog chooses to approach a person, the person should be calm and only pet the dog if the dog is calm and appears to want to be petted and use long slow strokes on the dog's side or scratch the dog's chest - no hugging, no petting the dog on the top of the head.

The person should never coax the dog to come over or try to lure the dog with treats. If the dog comes over, the person can give the dog a treat, but no luring. You want the dog to make the decision to go to the person.

This is not the time to have the dog in the same room where your 8 yr old boy and his 15 friends are playing. Or in the same room with your teenage girl and her 15 friends (way toooo much squealing(grin)).

Be calm, be relaxed. This is normal for dogs, although sometimes unnerving and upsetting to us. It will be over soon.

Sounds like it could be that but just in case I'd get her a checkup. Hope everything is ok.