Joyce Meyer is a "Word Faith" teacher.
It teaches: God created man in "God's class" (or, as "little gods"), with the potential to exercise the "God kind of faith" in calling things into existence and living in prosperity and success as sovereign beings.
We forfeited this opportunity, by rebelling against God in the Garden and taking upon ourselves Satan's nature. To correct this situation, Jesus Christ became a man, died spiritually (thus taking upon Himself Satan's nature), went to Hell, was "born again," rose from the dead with God's nature again, and then sent the Holy Spirit so that the Incarnation could be duplicated in believers, thus fulfilling their calling to be little gods.
Since we are called to experience this kind of life now, we should be successful in every area of our lives. To be in debt, then, or be sick, or (as is often taught) be left by one's spouse, and not to have these problems solved by "claiming" God's promises, shows a lack of faith.
Certain aspects of this doctrine can vary from teacher to teacher, but, the general outline remains the same in each case.
For her to say ""The amount of mercy you give other people is the amount of mercy that's going to come back to you" is nothing more than a word play on the Our Father in Matt.6. where it says: "And forgive us our debts, as we forgive our debtors"
No Christian is forgiven on the basis of forgiving others, we are forgiven, and cleansed when we judge our own sins and confess it to Jesus.
For if I by grace be a partaker, why am I evil spoken of for that for which I give thanks? Whether therefore ye eat, or drink, or whatsoever ye do, do all to the glory of God. Give none offense, neither to the Jews, nor to the Gentiles, nor to the church of God. Even as I please all men in all things, not seeking mine own profit, but the profit of many, that they may be saved. 1Cor 10:30-33
If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. 1John 1:9
If our forgiveness is conditional on forgiving others then the atonement of Jesus Christ (which wasn't even accomplished when Jesus taught the Jews to pray the Our Father) is insufficient, for "forgiveness and remission" of sins which is part of the finished work of Jesus Christ in the believer.
In whom we have redemption through his blood, even the forgiveness of sins: Colossians 1:14
A Jew under Jesus's earthly ministry (The Our Father), optained forgiveness on a conditional basis.