Magdalene's strong point is her vitality. Her naturally high health and her starting item, Yum Heart, allow her to survive more damage than other characters.
With her high number of heart containers, Magdalene can afford more deals with the Devil.
Magdalene's biggest disadvantage is her low speed, which makes her more vulnerable to threats, especially from fast-moving attacks and homing projectiles. Look to get items which increase speed and avoid those that lower it further.
Once the Aprils Foolchallenge is completed, this disadvantage is rendered moot as she will start every run with a Speed Up pill.
Favored Items
Items that trigger on player damage, such as Gimpy and The Virus, stand to see more action through Magdalene's high health.
Sacrificing health with an IV Bag can be quite useful if low on money.
A single speed boosting item such as The Belt will negate Magdalene's speed weakness.
If Aprils Fool has been completed, the Speed Up pill that Magdalene starts with will negate the weakness.
The AAA Battery trinket allows the Yum Heart to take only 3 rooms to charge instead of 4.
Guppy's Paw allows Magdalene to turn her four initial heart containers into twelve Soul Hearts - the maximum number of soul hearts possible.
The Habit and 9 Volt are blessings to Magdalene's regeneration if she still holds Yum Heart, as they allow the item to recharge itself much more quickly.
Old Bandage will have a chance to drop a heart upon being hit, which may come in handy if Magdalene's low on health.
Placenta's regenerative abilities can further supplement Magdalene's self-healing. The same applies for Little C.H.A.D.'s red heart generation and other similar healing items.
The Wafer is a godsend (no pun intended) to Magdalene's health-driven play style.
Shielding items can be used to compensate for Magdalene's low speed. (Infamy, Holy Mantle...)
Disfavored Items
Abaddon removes all red heart containers, which can turn out to be a disadvantage for Magdalene.
Bucket of Lard's heart container bonus is tempting, though it's better to avoid this item initially as it would render Magdalene's speed very low. Any other speed down items are to be avoided as well (Taurus may make an exception from its speed increase over time and My Little Unicorn effect if the speed becomes high enough).
Dark Bum eats red heart pickups, which can dampen Magdalene's regenerative play style. However, used in conjunction with her starting Yum Heart, Dark Bum can be a powerful way to turn otherwise redundant pickups to your advantage.
If Dead Cat is picked up early, it takes away Magdalene's primary strength (high health) and exacerbates her biggest weakness (low avoidance).
Bugs
Bug!
There are some stray pixels on Maggy's "Bad Pill" animation.
Trivia
Maggy appeared in the original Binding of Isaac.
Maggy's unlock requirements in Rebirth are the same in the original Binding of Isaac.
Magdalene is a reference to Mary Magdalene, a follower of Jesus who had seven demons cast out of her body, referenced with the seven heart containers needed to unlock her. She has been canonized as a saint in several Christian denominations, and is believed to have been a prostitute before following Jesus (though this has no textual basis in the Bible, and is considered by scholars to be a baseless myth).
In the game files, the image file for Maggie's hair is named maggiesbeautifulgoldenlocks.png.
Maggy's hair appears to be identical to the wig that Isaac receives in one of his mid-floor nightmares. It is possible the character of Maggy might be Isaac wearing a wig.
The person with gold hair in ending 14 and the Final ending has been confirmed to be Isaac wearing a wig, which furthers this idea.
Another piece of evidence is that the three female playable characters all have Isaac's voice.
Yum Heart.
If the Aprils Fool challenge is completed, she will also start with a Speed Up pill.
Bloody Lust.
Bug!
There are some stray pixels on Maggy's "Bad Pill" animation.
Magdalene Unlocks 
Characters 
The Binding of Isaac: Rebirth
