Limping Chicken - Antibiotics?

Hi there,

I have noticed one of my chickens (Betty) has started limping today and I have inspected her foot tonight and it's quite warm, mabye a little bit swollen but I can't see any cuts or injuries.  I want to nip it in the bud before it gets any worse and wondered if there are any antibiotics that I can buy off the shelf that I can put in the water or something?  I've been trawling the internet for about an hour but drawn a blank.  I don't really want to have to resort to taking her to the vets as the last time I did this it cost me £30 and I came back minus my chicken (Bertha!) .  Any advice would be appreciated. Thanks.

Thank you, I'll see how she is in the morning and give that a go if no improvement 

Experts:  Could Curries use Ibuprofen gel on the leg?

When my chicken started limping (I had seen her struggle to get on to a branch so did know the reason) I just left her and it took about a week for the limp to go - depending on what treats were being offered!