If she's looking just at the posting part, she should try Buffer/SocialPilot.co/HootSuite. That should do the trick. If she's looking to monitor for replies and engage with the community overall, then she might need to use more than one tool.
A quick Google search will find you lots of alternatives (apparently https://kuku.io/ as well as Buffer & SocialPilot that tejasm mentioned)
Also, do they do email as well?