Rules for throwing objects can be found in the Core Rulebook on page 209. As noted, a character may attempt to throw an object with a weight up to half their normal Lifting Weight. With a Space Marine's Unnatural Strength and Toughness, this means throwing anything up to 112kg (assuming a Strength and Toughness score of 40-49) would not be a problem. If her Strength and/or Toughness are 50 or higher, the maximum weight increases further. The relevant table can be found on page 208.
In the Deathwatch RPG, the average Space Marine clocks in at between 500 and 1.000 kg (see page 28), which very likely exceeds the character's normal throwing ability, so the test automatically becomes Hard and receives a -20 penalty.
Ultimately, your player thus needs to succeed on a -20 Strength test. If successful, the other Space Marine will gracefully ( ) sail through the air for a distance equal to the throwing character's Strength Bonus multiplied by any Degrees of Success the player may achieve. If the test fails, the other Space Marine will only fly a distance equal to half her character's Strength Bonus (so, probably still about 5 meters, due to the Unnatural bonus).
If the Space Marine is hurled at a specific target, he becomes an Improvised Weapon, and your player needs to test Ballistic Skill instead of Strength. Note that, as per RAW, this would make the test somewhat more difficult as her character no longer receives the bonus from the Unnatural Trait. Since this doesn't make a whole lot of sense (as her character doesn't get weaker just for tossing the Marine at something instead of anything), I would recommend houseruling that, for the purposes of this one action, she should roll on her Ballistic Skill, but still treat the result as if she had rolled on Unnatural Strength.
In either case, anything hit by the thrown Space Marine takes 1d10 plus the thrower's SB damage.
If you wish, you may also apply Falling Damage to the thrown Space Marine as per the rules on page 261, but due to the rules being a bit weird you may end up with the Marine taking more damage than what he was thrown at. Truth be told, I would probably houserule that whatever object or enemy the Marine is being hurled at takes a bit more damage, just due to the weight of this particular "thrown object".
 Oh, and don't forget to add the Strength bonus from power armour to the above tests ... I totally forgot to add the bonus damage from mine in today's game as I was busy punching Necron Scarabs left and right. Not that it mattered much; xeno constructs have such crappy craftsmanship.
Edited by Lynata, 14 December 2013 - 11:05 PM.