What happens if the commitment tx fee is too low?
Only if the state changes fees are negotiated (and for mutual closing the channel) so in case the onchain fees change and the channel is not used for a long time just send a fake payment hash to adapt to onchain fees.

Regarding 2 and 3. Nothing Alice can do. She just has to wait until the traffic on chain decreases. There are some ideas to include a dust level anyone can spend output to the commitment tx without timelock which could use cpfp