Shes a little safe right now, if she uses her silence correctly she shouldnt die often which leaves her free to heal form the backline. An example of someone who plays Soraka incredibly well is IMTs Adrian. His positioning is great.
Fortunately, Most Soraka players in low elo aren't the smartest and try to poke and be aggressive. Much like Jannas that try to use their tornado aggressively. When she steps up to poke in lane, getting a trade into her instead of the enemy ADC is generally the best way to hurt their sustain. Her Q poke is often predictable as well. And if you can dodge it, you can really shut her down. You definitely need to try to all in her thought if you want to beat her in the long run. Leona I've found does really well into Soraka, As does obviously Blitz. And even though she's fallen out of favor in higher elo play, Annie is the pup stomper of all pup stompers. Level 6 Tibbers that Raka and laugh straight to the bank with the kill you probably stole because you're paying Annie. Oops. Zyra is another good one for that. Theres plenty of things you can play into Raka. Her ulti can be game changing in team fights. but if its down thats a wonderful time to engage. She can only heal so much so quickly to a single target when her ulti is down. Raka forces the other team to be the aggressor, which is strong in the current meta where there arent as many hard engage champions seeing as the top lane is favoring Ekko, Graves, ect. She's in a good place more due to the lack of hard engage and a lot of peoples inability to focus. But that's just my opinion as a former dirty Soraka main.