If a long leash is too heavy for her to drag around you can always go to a hardware store, buy a clip that is used on a leash and attach a length of laundry cord to it (the string people use to hang their laundry to dry).

I always use my 30' leash with dogs I am babysitting, or dogs I can't trust. I hate flexis so a drag line is a much better (for me) option.

Here's a pic of a papillon I took care of running with a drag line.


And here's a pic of a beagle with the 30 foot leash attached.


One other option is you can attach your dogs together if you are sure one will listen. I used to do this with my grandpa's pug. I'd attach him to Emily on a very long line because I know Em will listen.