The 21-year-old picked up the injury racing at an event in Belgium.
"Local doctors told me it takes four to six weeks to recover and I shouldn't really be riding my bike," Garner told BBC Radio Leicester.
"But I have spoken to sports doctors and they said whenever you feel you can ride, then you can. I only had one day off, then I was back on the rollers."
Garner, who rides for the Wiggle Honda team, crashed in the Keukens van Lommel Ladies Classic race in Herselt.
"I had just started the race," added Garner. "I was actually at the front of the peloton, making sure I was ready for any attacks that might happen.
"Suddenly I saw this girl just in front of me and she just flew to the left. I was on the right and although I had to move a little bit, I thought I would miss it.
"But suddenly I found myself over the handlebars, flying to the other side of the road, and I just landed straight onto a barrier with my ribs.
"I knew straight away something wasn't right and I had a lot of pain. I was on the floor gasping for breath and I knew it wasn't good and I needed to go to hospital."
Despite Garner being back on the bike, the injury means she is missing from the Women's Tour which got under way on Wednesday.
"This is most serious injury I've had," added Garner. "I knocked a few teeth out when I was 12 on my bike.
"But I can already manage three hours on the bike on the road. I am actually happy with how it is going considering it has been just over a week."
Leicester cyclist Lucy Garner says she is already back in training, despite breaking two ribs only a week ago.