Toddler jealous of 7 month old

[Girlsville]

Help please! I have a 15 month age gap between my two girls. DD2 is now 7 months and DD1 is 22 months. From day one DD1 has always been amazing with DD2, no jealousy, no signs of being unsettled, and generally being very attentive and loving to her. In the last month however DD1 has become increasingly clingy to me (not wanting anything to do wth DH to is great upset) and then in the last three days has started to show lots of green eyed monster. She shouts "mummy no hold DD2" whenever I hold DD2 and has a tantrum.
Not sure why the jealousy has suddenly appeared when she was amazing about it for 7 months. What do I do? DD1 gets plenty of one one one time with em every day when DD2 naps and after DD2 goes to ebd, and I also sit down with her to do colouring/play doh etc at least once a day while DD2 is awake.
DD1 generally also being very tantrummy at the moment, screaming when she doesnt get her way. I know she is entering terrible twos but still!. AHHHH!

is the baby becoming more mobile?

IME a baby lying down, doing nowt isn't really worth bothering with, from an older child's PoV but suddenly once they start doing stuff it's like an UH-OH for the older one

The bby isnt eyt mobile, although sitting a bit. But she is obviosuly more interactive, more demanding , eating at the same time and generally ebcoming more of a person!! Any tips on how to handle the jealousy?
When I was out at a playgroup last week DD! started screaming and crying ""DD2 floor". In my panic I threw DD2 into the arms of a friend and picked p DD1 to comfort her. .....now worried that I have just reinforced to DD1 that she can just cry and scream and I will put DD2 down . But just wanted to make dd1 feel secure!