You poor thing! It is so frustrating and tiring! My little one did this from the day dot and I only got her to go to sleep at around 6 months! If you think it is a wind problem ( my cherub had severe colic) you could try Colic Relief by Brauer as it helps soothe their little tummy and is very gentle unlike some other colic formulas. It may also be worthwhile having her checked out by a peadiatrician to rule out anything like reflux etc...  Even the most persistant cherub will crash and burn after 30 to 40 minutes heart breaking sobbing. Keep your chin up and I hope it resolves soon!

Hi my daughter was the same. it took 6 weeks of persisting. first step is to have a sleep routine milk,play,read sleep, may be a teddy in the cot. when putting child down do the same every time. place child in cot leave the room immediately. Let baby cry for 5 mins go in pat on the shoulder and leg until crying stops then leave the room. Next time go in after 7 mins do the same again, then leave the room, do again next time do 7 mins. If still crying pick up to see if there is any wind. Once baby stops crying do the process again. don't break the cycle I know it can be testing and heart breaking. i now have a perfect self soothing child, has two day 1 and half hours sleep and sleep 12 hours at night without waking.

If I can remember, at 7 months, they are just learning to crawl. You may want to tire her out a little more than you have been before this nap. I would put her on her tummy more, and have her reach a toy from your 3 yr old to include him, or put her in her exersaucer for more time, or a kicker toy. Just tire her more before the nap. Also, for my girls, I have always put on lullabye music to drown out the rest of the house noises and put it on repeat, made the room dark with dark curtains, and my monitor displayed a light show in the ceiling. For my first child we had a "momma bear" in her crib that when turned on sounded like my heartbeat.  . And to make things more interesting, they usually do drop the morning nap at about 1 year and go to only one nap.  Good luck. Hope this helps