It wouldn’t work due to bandwidth limitations as you’re guessing.
If you want your photos accessible from various locations then you carry them with you on a few external hard-drives.
I do this between home and work every day so I always have my working set of photos available.
I back up my external hard-drive to another external hard-drive every night, or just after copying a big set of photos to it, so I always have more than one copy in case something happens to the external hard-drive, either from damage or losing track of it.
Is this person planning on carrying a computer with her that has the LR program and LR catalog or is she expecting to install the cloud LR everywhere she goes?
To my knowledge LR the program can't be installed on a server to be accessible from multiple computers. It has to be installed to each and every computer you want to run it on.
As for the LR Catalog Adobe has restricted that also so you must maintain a local catalog file on each computer, IE you can't put the Catalog on a Networked drive whether a local network, LAN, or one accessed across the net, WAN.
So the only way for your client to have access to all her images from anywhere in the world is to either copy all images and the catalog to the computer she is using, along with having LR installed, or setting up LR to make Smart Previews of all her images and just copying the catalog tyo the computer she is using, along with having LR installed on that computer.
In other words what she wants isn't going to happen.
Lightroom cannot be on a server as has been stated.
However I would suggest putting the catalog on an external drive and building smart previews of all the files. This allows for working on the files via the smart preview with the changes being carried to the raw/master files when they are available. This is one of the design uses of smart previews.
However to fully answer it would help to know why access to all files is wanted.