Breastfeeding help

Hi everyone!

So I just had my second daughter on June 2nd. She instantly latched on with a nipple shield (flat nipples, and I’ve also tried a manual pump to pull my nipples out but it’s still not enough for her) but she lost an entire pound in 3 days so I got discouraged and resorted to pumping.. so I’ve been pumping for almost 4 weeks now.. only pumping around 2oz everything 3-4 hours so I’ve had to supplement around 1-2 formula bottles a day starting when she was around 1 1/2 weeks old. Well now that she has gained back a little over 10oz now, I decided to put her back to the breast with a nipple shield.. (tried again without and she wouldn’t latch) and she’s latching but I don’t feel like it’s a good deep latch because I’m having to hold my boob to her for her to stay on. I can feel her sucking (it doesn’t hurt) and their is milk in the nipple shield when she’s finished so she’s getting something out. How can I help her get a better latch with the nipple shield to ensure she is getting a good latch to get enough milk?