If your account is issued in the USA there is no ability to combine points with any other person's Membership Rewards account.

If your wife holds an additional card on your account the points earned with that card are automatically credited to your Membership Rewards account.

If your wife has her own American Express cards which earn Membership Rewards points she can add you as a additional cardholder, and this will allow her to Transfer points to your airline or hotel accounts , but not to your Membership Rewards account. Note that she cannot transfer to your accounts until the additional cards have been open for 90 days.

Discussion here:

AMEX (USA) kills ability to transfer MR to non-account holder's airline or hotel acct