> is it too soon to put the wire fence back up?<
No...... Go ahead and put the fence wire back up and working to insure that your Beag dose not get out and get hurt/injured.
>unattended 30ft tether<
I would take a close look to make sure there is no way for Molly to get tangled up with tether line and cause injury.
>saying NO stops her from digging<
This is a good sign and shows understanding the word no and recognizes you as authority. I would start working on basic obedience ( sit , down , stay ) using treats and lots of praise for correct behavior while on walks and some just having fun time and take it slow and keep it friendly and fun. This will serve as the building blocks for all sorts of training , plus , it is a great bonding tool.
>Also, would bicycling with Molly be a good idea or should I wait till we have more walks behind us?<
If it were me , I would take a couple of weeks to continue with light basic obedience training and bonding while your girl settles in to her new environment , this will pay off big with all future work with Molly.
As for the bicycling with Molly. This is a question that only you will be able to answer. For example: I do not know how much physical work Molly can handle at one time without being overheated or stressed. I would proceed with caution and take along water for Molly and not do too much at one time. Just keep things fun as she adjusts to whatever type of physical activity you choose. Important Note : Make sure no food 1 hour before or after heavy physical output and make plenty of cool water available for Molly.
Best , oldhounddog