That's a tough one since she's living outside.
Usually I'd recommend keeping the legs bandaged constantly. Taking the bandages off only when you're going to be icing and hosing the leg (which should be done as often as possible).
Since bandaging isn't an option in this case, I'd invest in lots of arnica oil to massage into the splints. Not only will this help with the swelling, but by keeping the circulation going it is possible to lessen the resulting blemish and helps the splints to go down more.
If the inflammation is as bad as it sounds, I'd say you should contact your vet to get her some anti-inflammatories.
I'd also speak to your barn owner about working some kind of deal for your horse to stable, overnight at least, just until the splints settle. Otherwise you're going to end up with huge blemishes that will be even more difficult to get rid of.
It is not 'cool' to ride without a helmet! period.