'out of shape' and needing advice!

Hi there! So I'm new to this forum and would really appreciate if someone could listen to my story and help me out! So I swam in college and graduated last May(yes I'm a youngster). I took a full year break from swimming and any exercise what-so-ever. Literally was a couch potato for a year, felt so good. Anyways, I just joined a masters team and started going to practice about a month ago. I started slow and only went 2 times a week and now I'm up to 4 times a week. The masters team I practice with does about 3,500-4,000 a practice. I'm really out of shape(I know, in comparison to those who have taken a decade or more out of the pool, maybe not so much), and I don't know how to put together a reasonable timeline or expectations of how long it will take me to get back to where I was. My slowness is demoralizing, and I know I have to be patient, but is it unreasonable to think I'm going to get back in shape and go close to my best times further down the road with only doing 4,000 a practice? Should I do more? I've never taken so much as a month off of swimming, so the whole getting back in shape thing is new to me. Just as a background, I'm a female, and swim butterfly(58 in the 100, 2:07 in the 200) but I can barely do a 25 fly without feeling like my arms are going to fall off! Does anyone have suggestions of how to get back in reasonable shape or some kind of timeline? Thanks! I really appreciate any input!