Hugs for the short naps. I agree, she's not getting enough day time sleep. When my dd was short napping, I would APOP one nap during the day. So usually I'd try to extend her nap (like you, I'd try for 20 min or so) nadir that failed, I'd APOP the second nap so that she got at least one decent nap in.
Now for extending naps, I would go in before she was going to wake, so try at the 20 min mark, and I would start to shh her when she started to squirm. I didn't pu unless I had to but usually that meant the nap was over when she was older than 3 mo. Hang in there!