The approach I've used successfully is to automate the enabling and disabling of a dedicated group for the devices to be controlled. The broad steps are as follows, adjust as needed.
Starting with a default Pi-hole setup... you, your daughter, all devices are getting the blocks from your blocklists and any custom domains/regexes added. Everything is in the Default group. You want just your daughter's devices to have additional domains blocked at certain times.
In Groups create a group called Daughter
In Domains add the exact and regex domains that you want to block, adding them to the denied domains. For each domain, edit its Group assignment so that it is in only the Daughter group, ie there is a single tick only next to that group in the box. You can do this as you add them or scroll down and do them afterwards.
In Clients add all your daughter's devices and, for each one, edit its Group assignment so that it is in both the Default and the Daughter groups, ie there is a tick next to both groups in the box.
This means all the devices using Pi-hole on your network get the behaviour from the Default group as originally. Your daughter's devices also get the behaviour from the Daughter group as well, because she is in both groups. And that behaviour is just some additional domains and or regexes set to denied.
In Groups test toggling the Daughter group on and off. When it's off she is back to having just the Default group behaviour. When it's on she gets the Daughter group rules too.
Finally create root cron entries to toggle this as desired. For example turning the group on at 9am Mon-Fri and off at 6pm Mon-Fri. On the Pi-hole:
sudo crontab -e
#Enable Block:
0 9 * * 1-5 /usr/bin/pihole-FTL sqlite3 /etc/pihole/gravity.db "update 'group' set 'enabled'=1 where name='Daughter';"; /usr/local/bin/pihole reloaddns &>/dev/null
#Disable Block:
0 18 * * 1-5 /usr/bin/pihole-FTL sqlite3 /etc/pihole/gravity.db "update 'group' set 'enabled'=0 where name='Daughter';"; /usr/local/bin/pihole reloaddns &>/dev/null
Note – It's worth pointing out that, while this can help with casual access, Pi-hole isn't a parental control device so please don't rely on this to manage device access or individuals' behaviour. And note that devices can work around Pi-hole, eg using external DNS.