Hi Sasha, I would think it's way too early to be thinking about exercise. Give it two or three weeks and then institute a gentle routine - gradually building up to get that heart rate up - you're not currently taking in enough calories to sustain an exercise routine.
Are you Sole Source? All of your meal replacements have been carefully calibrated to do one thing only: encourage your body to burn stored fat reserves. Give your body a wee bit of a chance to get used to the new regime .... There will be time enough to tone those thighs, I promise, just focus on one day at a time 100% SS; when your body acclimatises in a few weeks (and you trust the losses on the programme more, so won't mind seeing a gain of a lb of muscle instead of lost fat!) you can start gentle leg lifts, treadmills etc.
Right, all that is out of the way so I just have to say: Well done on making this choice to fight for and rediscover beautiful you

Welcome aboard .... It's not for the feint of heart, but the rewards of the plan are phenomenal. I look forward to hearing about all your successes x