Never force a dog to swim, especially if you are inexperienced.
While some Cocker Spaniels are brilliant swimmers, but the wrong method, a drowning dead.
If she is really reluctant, you may stick with tiny water areas and don't force it.
Start with washing her down with a sponge and water.
Praise her when she relaxes.
If she calms down with sponges and water, move to hosing, it may take longer, but give her treats/praise and she'll think 'great! when I let them put water on me i get a pet/treat!'
Walk her over puddles, small, but one step closer. or make your own little water area.
If you can get one of those kiddie pools and show her they're fun.
Gradually move up to larger water parts.
Never throw your dog in the water unless you are 100% confident it can swim, it enjoys it and is a bigger dog bred for swimming.
She may have suffered a traumatic experience in water so take it easy and show her that involvement with water =treats, fun and fetch!
Toss a toy into a puddle, into a kiddies pool, into a wet area and then toss it into a tiny pool, river.