Finding Inner Strength..?

It depends on your problem. The more you feel vulnerable and helpless, the more you lose your sanity.
Stress is fine if it is there for sometimes. But it can affect your health if you are stressed for a long time.

First of all, having self confidence is very important.
Whoever the trouble makes, be it your husband or in laws or outsiders, just be confident about yourself.
Please have confidence on your ability to face the problems, and face the life after confronting the problems if necessary.
Secondly, self dependence is important. Yes, we always say marriage is all about interdependence. It is good to depend on your spouse and his family after officially joining them. But that is not really helpful when they are not-so-great people.
Your dependency could eventually make you vulnerable.
So, depend on yourself. Both financially, and physically.
Make own finances, own set of friends or reliable people and a social life for yourself while being married. It gives you the sense of independence and confidence to face any kind of issues in life.

And finally acceptance is important. Every person is unique and they will have their own set of reasons for their behavior.
If your MIL is evil, she may have a reason for it. Her greediness, selfishness, harsh nature etc..etc.. has a reason which we often ignore. Yes, she may be aging, she may be combating menopause, she may be ignored, she may have insecurity, she may be brainwashed by others. Even if not, acceptance helps. Accept as who she is.
Don't try to change her or expect any miracles to bring about changes in her.
Instead, be the change.

I do not mean to change yourself as per MIL's expectation. No...
But change to a strong person, so that you won't be affected whenever your MIL taunts you.
Change your attitude to be positive, and change to be a flexible person in order to accommodate other's opinion without any grudges.
You learn to ignore when negative things come your way.

This way, you will have less problems to face.

 

Get indulged in something which you like more... It could be as simple as browsing, reading or listening to music. And give urself more time.
Then as SGBV said leave good and bad to them. There is no need to develop anxiety on this. Because if not one tomorrow there will be another one. If anyone is creating issues verbally or emotionally, become more stronger and stay away from them as much as possible.
And finally to make an attempt to be in their good books by taking extra efforts. That will never happen.